Method for fabricating semiconductor laser device by aligning semiconductor laser chips based on light emission measurements

ABSTRACT

After profiles of two chips are recognized on intermediate stages and their positions are corrected, collets are used as electrodes and a voltage is applied to the chips on bonding stage on which the chips are bonded onto a submount. Then, the respective two chips are allowed to emit light, final position correction is performed on the basis of the light-emission point data and bonding is performed. The two chips can be bonded at narrow pitches by tilting the collets with respect to chip surfaces. Consequently, two laser chips can be bonded at narrow pitches on one submount in high position accuracy.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and a method for bondingtwo semiconductor laser chips at narrow pitches on one submount in highaccuracy. The present invention is utilized in an apparatus for bondingthe two laser chips (for example, combination of a red chip and aninfrared chip or the like) such as a combination laser die-bonder or thelike.

One example of a conventional one-chip bonding apparatus is explainedbelow. Conventionally, a semiconductor laser chip 4 is vacuum-sucked byusing a vertically provided vacuum-suction collet 6, peeled from a wafersheet 1, transferred to an intermediate stage 2 and passed as shown inFIGS. 1 and 2. On the intermediate stage 2, a chip profile is recognizedby image processing and then, a light-emission axis is recognized. Achip position is corrected in X, Y and θ directions on the basis of thisdata.

After the chip position is corrected in the X, Y and θ directions on theintermediate stage 2, the chip is sucked again by using the suctioncollet 6 and transferred onto a submount 5 placed on a bonding stage 3.The chip is bonded onto the submount 5 as it is with an adhesive or bythermo-compression bonding.

That is, the chip position is corrected only on the intermediate stagein the above-described conventional one-chip bonding apparatus.Therefore, when the chip is passed to the submount by using the colletafter the position correction on the intermediate stage and the chip ismounted on the submount, a fine shift occurs. Thus, bonding positionaccuracy according to a specification (±2 μm or less) could not beensured, thereby resulting in variations in a laser direction.

A method of efficiently fabricating a semiconductor laser withoutvariations in a light-emitting direction in a die-bonding process of asemiconductor laser is disclosed in Japanese Patent Laid-OpenPublication No. 7-202347. In this method, a laser chip is energized andallowed to emit light on the intermediate stage by using a probe. Alight-emission axis direction is measured by image processing and thelaser chip position is corrected on the basis of the measured value.When the light-emission axis direction is within a certain error range,the laser chip is sucked and transferred by a laser chip feed mechanismfor die-bonding. Thus, the chip position accuracy is improved.

When a two-chip semiconductor laser device is fabricated, two kinds oflight-emitting chips having different wavelengths are bonded on onesubmount with favorable accuracy. The chips 12, 13 are bonded one by onein FIG. 3A. When the second chip 13 is bonded, heat is applied to thefirst already bonded chip 12 at its junction and the clip 12 comes off.Therefore, the two chips need to be bonded at the same time.

In FIG. 3B, two conventional collets are simply arranged in a mirrorimage to constitute a two-chip bonding by using the one-chip bondingapparatus in FIG. 2 so that two laser chips are die-bonded on asubmount.

Since a specification for a distance between light-emission points is100±2 μm in the two-chip semiconductor laser device, the chips need tobe bonded so that a distance between the respective light-emissionpoints 14, 15 of the two laser chips 12, 13 is 100±2 μm as shown in FIG.4. It is shown, however, that, since the collets are vertically disposedin a constitution shown in FIG. 3B, the collets interfere with eachother and thereby the two chips cannot be bonded closely.

In the method disclosed in Japanese Patent Laid-open Publication No.7-202347 as well, it is shown that, since the collets are verticallydisposed, the collets interfere with each other and thereby the twochips cannot be bonded closely.

To prevent the collets from interfering with each other in theconstitution where the collets are vertically disposed, a diameter ofthe main body of a collet might be made thinner than the chip profile.However, currently the diameter of the main body of the collet cannot bemade thinner than the chip profile because a vacuum hole forvacuum-sucking a chip needs to be provided, rigidity larger than acertain level is required due to a load applied upon chip suction andchip bonding and the collet needs to be shaped so that position accuracyin attachment/replacement of the collet can be easily ensured.

As described above, when the above conventional devices are simplyarranged laterally in a mirror image when a semiconductor laser devicein which two laser chips are die-bonded on a submount is fabricated,there are disadvantages described below.

(1) Since the position is corrected only on the intermediate stage, afine shift occurs after the correction on the intermediate stage whenthe chip is passed by using a collet or the chip is placed on thesubmount.

(2) The specification required distance (x in FIG. 4) between thelight-emission points of the two chips is as narrow as 100 μm.Therefore, when the two chips are bonded at the same time, the normalvertical collets interfere with each other and thereby the two chipscannot be bonded at desired positions at the same time even if thelight-emission point is positioned as closely to an end of the chip aspossible.

SUMMARY OF THE INVENTION

The present invention was accomplished from the above viewpoints.Accordingly, an object of the present invention is to provide anapparatus and a method for bonding two semiconductor laser chips on onesubmount at narrow pitches in high accuracy.

In order to achieve the above object, there is provided a method offabricating a semiconductor laser device wherein two semiconductor laserchips are die-bonded on one submount, comprising processes of placingthe semiconductor laser chips on intermediate stages, allowing thesemiconductor laser chips on the submount to emit light and measuringlight-emission point positions and transferring the semiconductor laserchips through fixed points to prescribed positions on the submount.

That is, in the present invention, a position of each semiconductorlaser chip is corrected by profile recognition and light-emission axisrecognition on the intermediate stage, a voltage is applied to each chipby using a collet as an electrode on a bonding stage for bonding thechip on the submount to allow each of the two chips to emit light, thelight-emission point position data is subjected to image processing, theposition of each of the two chips is finally corrected by ahigh-resolution precision positioning mechanism driven by apiezo-electric element of a bonding head on the basis of the data andthen bonding is performed. Thus, according to the fabricating method ofthe present invention, a two-chip semiconductor laser device can befabricated in high bonding accuracy.

In one embodiment of the present invention, the method comprises aprocess of measuring light-emission point positions and light-emissionaxis directions of the semiconductor laser chips placed on theintermediate stages.

In one embodiment of the present invention, the method comprises aprocess of correcting positions and directions of the intermediatestages on the basis of the results of measuring the light-emission pointpositions and light-emission axis directions of the semiconductor laserchips placed on the intermediate stages.

In one embodiment of the present invention, the method comprisesprocesses of sucking the two semiconductor laser chips from respectivewafer sheets or a chip tray by using collets, transferring the colletsthrough fixed points by a fixed-point transfer movement mechanism andplacing the two semiconductor laser chips on the respective intermediatestages, correcting positions of the two semiconductor laser chips on therespective intermediate stages, sucking the two semiconductor laserchips again, transferring the chips through fixed points and mountingthe chips on the submount, energizing the two semiconductor laser chipson the submount to allow the chips to emit light and measuring adistance between the light-emission points of the two chips.

In one embodiment of the present invention, the method comprises aprocess of transferring the two semiconductor laser chips onto thesubmount through fixed points and then correcting the chip positions onthe basis of the measured distance between the light-emission points bya movement mechanism for fine XY movement provided separately from thefixed-point transfer movement mechanism.

Therefore, according to the present invention, two chips are once placedon respective intermediate stages, a profile and a light-emission axisof each chip are recognized by a camera, the chip position is correctedby image processing and the chip whose position is corrected istransferred onto a submount through fixed points from left and right.Therefore, a shift on the submount occurs only when the chip is passedafter the profile recognition. Therefore, light-emission points of thetwo chips can be easily recognized even in a narrow visual field of ahigh-magnification camera.

When the chip position is not corrected on the intermediate stage, thetwo chips may hit each other due to a large shift upon pickup of thechips since the gap between the two chips is narrow. However, this canbe prevented.

Since the distance between the light-emission points of the two chips onthe submount is measured to confirm that the chips are at prescribedpositions and then thermo-compression bonding is performed, bonding canbe performed in high accuracy.

That is, according to the present invention, positions of the twosemiconductor laser chips are corrected on the intermediate stages byimage processing. Since the distance between light-emission points ofthe two semiconductor laser chips is further measured on the submount tocorrect the positions, bonding can be performed with a more accuratedistance between the two chips as compared with a conventional methodwherein the chip position is corrected only on the intermediate stage.

When no problem occurs upon the above-described pickup of the chip, theposition can be roughly corrected on the intermediate stage.Consequently, a process time can be shortened on the intermediate stageso that the apparatus tact can be shortened.

In one embodiment of the present invention, the method comprisesprocesses of allowing the two semiconductor laser chips to emit light onthe submount at the same time, measuring a distance betweenlight-emission points and using one light-emission point as a referenceand moving the other chip to a prescribed position on the basis of themeasurement data.

According to the above embodiment, bonding can be performed accuratelyand the apparatus can be constituted at a relatively low cost, sinceonly one chip bonding head needs to have a fine adjustment mechanism.

In one embodiment of the present invention, the method comprises aprocess of allowing the two semiconductor laser chips to emit light onthe submount, measuring a distance between the light-emission points andmoving both the chips to prescribed positions by using light-emissionpoint positions predetermined for both the semiconductor laser chips asreferences on the basis of the measurement data.

According to the above embodiment, bonding can be performed accuratelyand, by providing both the chip bonding heads with a fine adjustmentmechanism, not only a relative position between the two chips, but alsoan absolute position of each laser chip with respect to the submount canbe determined in high accuracy.

Also, there is provided a two-chip bonding apparatus for die-bonding twosemiconductor laser chips on one submount, having intermediate stagesfor correcting positions and directions of the semiconductor laserchips, a bonding stage for placing a submount on which the semiconductorlaser chips are bonded, means for allowing the two semiconductor laserchips to emit light at the same time on the submount placed on thebonding stage, means for measuring a distance between light-emissionpoints of the two semiconductor laser chips and means for transferringthe two semiconductor laser chips through fixed points to prescribedpositions on the submount.

In one embodiment of the present invention, the apparatus has colletsfor sucking the semiconductor laser chips, a fixed-point transfermovement mechanism which is connected to collet heads of the collets tomove the collets, means for recognizing profiles of the semiconductorlaser chips on the intermediate stage, means for recognizing lightemission axes of the semiconductor laser chips on the intermediatestages, a drive mechanism for correcting positions and directions of theintermediate stages, means for allowing the two semiconductor laserchips to emit light at the same time on the submount placed on thebonding stage and means for measuring a distance between light-emissionpoints of the two semiconductor laser chips, and which correctspositions of the two semiconductor laser chips on the submount and thenperforms bonding.

The conventional collets are vertically disposed as shown in FIGS. 1 and2. On the other hand, in the present invention, the collets are disposedwhile tilted towards both the front and lateral directions of the deviceas shown in FIG. 5A so that the collets do not interfere with each otherupon die-bonding of two chips. Thus, die-bonding can be performed infavorable accuracy with a gap between the light-emission points of 100μm.

Therefore, a tilted-type collet 16 whose end is ground so as to be inparallel to the chip surface was developed in the present invention sothat a chip could be sucked while the collet is tilted. FIG. 6 shows anenlarged view of the end portions of the tilted-type collets of thepresent invention.

In such an eccentric-type collet 17 as shown in FIG. 5B, die-bonding canbe similarly performed in favorable accuracy with a gap between thelight-emission points of 100 μm. This eccentric-type collet 17 isobtained by soldering an eccentric block to a conventional collet todeviate the collet end from the center. Thus, collets are prevented frominterfering with each other.

In one embodiment of the present invention, a piezo-electric elementprecision drive mechanism for fine XY movement is separately connectedto the collet heads separately from the fixed-point transfer movementmechanism.

According to the above embodiment, in each of the bonding heads for ared chip and an infrared chip, a precision positioning mechanism (apiezoelectric element precision drive mechanism is further provided on ablock driven by a ball screw in the XY direction and the collet isdisposed at its ends.

In one embodiment of the present invention, the piezo-electric elementprecision drive mechanism is driven on the basis of the measuredlight-emission point distance data.

In one embodiment of the present invention, the collets are tilted-typecollets, the two tilted-type collets are attached as opposed to eachother and the two semiconductor laser chips can be die-bonded at thesame time by using the two tilted-type collets.

According to the above embodiment, the two respective semiconductorlaser chips can be made close to each other while vacuum-sucked. Thus,two-chip die-bonding with a fine gap can be achieved.

That is, in the two-chip bonding apparatus according to the presentinvention, chips are transferred through fixed points onto the submountby using the opposed tilted-type collets 16 shown in FIG. 5A and thechips are allowed to emit light on the submount. Each position iscorrected by using a piezo-electric element on the basis of thelight-emission point recognition data. Thus, die-bonding can beperformed by the two collets in favorable accuracy.

In one embodiment of the present invention, a visual field is opened byusing the opposed tilted-type collets as the collets so that a chipbonding state and a collet suction state can be confirmed from rightabove the chip bonding head.

According to the above embodiment, when the collets of the presentinvention are used, a bonding state can be confirmed from right above.The positions or bonding situations of the two chips can be monitored bydisposing the camera right above the chips.

In one embodiment of the present invention, the collets areeccentric-type collets, the two eccentric-type collets are attached asopposed to each other and the two semiconductor laser chips can bedie-bonded at the same time by using the two eccentric-type collets.

According to the above embodiment, the two semiconductor laser chips canbe made close to each other while vacuum-sucked. Thus, die-bonding oftwo chips with a fine gap can be achieved.

That is, in two-chip bonding apparatus according to the presentinvention, chips are transferred through fixed points onto the submountby using the opposed eccentric-type collets 17 shown in FIG. 5B and thechips are allowed to emit light on the submount. Each position iscorrected by using a piezo-electric element on the basis of thelight-emission point recognition data. Thus, die-bonding can beperformed in favorable accuracy by the two collets.

Therefore, according to the above constitution of the present invention,the resolution for positioning during the fixed-point transfer may belower than a resolution required in the final position correction. Thecollets can be moved at a high speed during the fixed-point transfer.Thus, production efficiency can be improved.

When a position resolution is required in the final position correctionbetween the two light-emission points on the submount, a high-resolutionand accurate positioning can be achieved by a piezo-electric element.

In one embodiment of the present invention, a pair of collets areprovided for each of the intermediate stages and the bonding stage.

According to the two-chip bonding apparatus of the present invention,since a pair of collets are provided both for the intermediate stage andthe bonding stage, position correction on the intermediate stage andposition correction on the bonding stage can be performed at the sametime. Thus, the apparatus tact can be shortened.

To allow a chip to emit light, a probe needs to be brought into contactwith the chip surface. In a conventional device, however, it was harddue to a small size of the chip to allow the laser chip surface to bebrought into contact with a probe while the chip is being vacuum-suckedby a collet. However, when the collet is made with an energizingmaterial and the collet itself is made with an energizing electrode, thelaser chip can be energized and allowed to emit light whilevacuum-sucked.

Therefore, in the two-chip bonding apparatus of the present invention,the collet is fabricated with an energizing material and used as anelectrode for allowing the chip to emit light. The chip is allowed toemit light by applying a voltage to the collet.

According to the present invention, the collet is lowered while a laserchip is vacuum-sucked and mounted on the submount. The suction colletand the ground side on the submount can be energized so that the chip isallowed to emit light.

In one embodiment of the present invention, the collets are fabricatedwith a tungsten cobalt carbide (WC—Co) superhard metal sinteringmaterial, the collets are used as chip light-emitting electrodes and thechips are allowed to emit light by applying a voltage to the collets.

According to the above embodiment, since the collet is used as a toolfor subjecting the semiconductor laser chip to thermo-compressionbonding and as an electrode, the collet needs to have low thermalconductivity and high electric conductivity as well as high componentrigidity and high component accuracy. Therefore, the inventors of thepresent invention paid attention to a WC—Co superhard metal sinteringmaterial as a material of the collet.

A WC—Co superhard metal sintering material has low thermal conductivity.Since heat does not easily escape through the collet uponthermo-compression bonding of the laser chip, this material is effectiveas a material of the collet. Due to relatively favorable electricconductivity, this material can also be used as an electrode.Furthermore, since the WC—Co superhard metal sintering material has highrigidity, a fine component having high accuracy and high rigidity can befabricated by electric discharge machining.

Bonding in higher position accuracy could be achieved by using themethod and the apparatus of the present invention as compared with aconventional die-bonding apparatus where chip correction is performed byimage processing only on the intermediate stage.

That is, according to the present invention, when two semiconductorlaser chips are die-bonded on one submount, the chips can be mounted inhigh accuracy with a distance between light-emission points of the twochips within a range of 100±2 μm Furthermore, since final positioncorrection is performed on the submount, collets can be moved at highspeed during fixed-point transfer. Thus, productivity can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a schematic view showing a constitution of a conventionalone-chip bonding apparatus;

FIG. 2 is a schematic view showing one example of the conventionalone-chip bonding apparatus;

FIG. 3 is schematic views showing two-chip bonding using conventionalcollets,

FIG. 3A is a schematic view showing a process of bonding chips one byone, and

FIG. 3B is a schematic view showing a process of bonding two chips atthe same time;

FIG. 4 is an explanatory view showing a bonding situation of a submount,a red laser chip and a infrared laser chip of a two-chip semiconductorlaser device;

FIG. 5A is a schematic view showing tilted-type collets of the presentinvention and

FIG. 5B is a schematic view showing eccentric-type collets of thepresent invention;

FIG. 6 is an enlarged view showing ends of the tilted-type collets ofthe present invention;

FIG. 7 is a schematic view showing a constitution of the two-chipbonding apparatus of the present invention;

FIG. 8 is a schematic view showing one example of the two-chip bondingapparatus of the present invention;

FIG. 9 is a schematic view showing one example of position correction onan intermediate stage according to the present invention;

FIGS. 10A-10C are schematic views showing one example of positioncorrection on the intermediate stage according to the present invention;

FIGS. 11A-11D are schematic views showing one example of positioncorrection on the intermediate stage according to the present invention;

FIGS. 12A-12D are schematic views showing one example of positioncorrection on the intermediate stage according to the present invention;

FIG. 13 is a schematic view showing one example of position correctionon a bonding stage according to the present invention;

FIG. 14 is a schematic view showing one example of position correctionon the bonding stage according to the present invention; and

FIG. 15 is a view with detailed dimensions of the eccentric-type colletof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The operation procedure of bonding a red chip and an infrared chip byusing a two-chip bonding apparatus of the present invention shown inFIGS. 7 and 8 includes the following processes:

(1) Positions of chips to be removed from respective wafer sheets 101,102 for a red chip and an infrared chip are confirmed by imageprocessing and these chips are positioned at prescribed positions;

(2) The chips are lifted by a lifting flash, vacuum-sucked by collets105, 106 and removed from the wafer sheets 101, 102;

(3) The chips removed from the wafer sheets 101, 102 are transferredthrough fixed points while vacuum-sucked and then placed on intermediatestages 109, 110;

(4) Chip shift amounts x and y from the prescribed positions of thechips are detected by using profile recognition cameras 111, 112 andangular shift amounts θ are detected by light-emission point recognitioncameras 113, 114;

(5) The intermediate stages 109, 110 are moved by shift amounts x, y, θby an X, Y, Θ drive mechanism (not shown) so that the chip positions arecorrected to the prescribed positions;

(6) The chips whose position is corrected are vacuum-sucked by thecollets 105, 106 and transferred through fixed points from left andright until positioned to positions above a submount 116 placed on abonding stage 115; and

(7) The collets sucking the red chip and the infrared chip 103, 104 fromleft and right, respectively, are lowered so that the chips are broughtinto contact with the submount 116.

The above processes (1)-(6) can be performed for a red chip and aninfrared chip at the same time or one by one. In a conventional device,process (7) cannot be performed at the same time. However, this processcan be performed at the same time in the present invention.

In the conventional device, bonding is performed here and then theprocedure finishes. However, the present invention further includes thefollowing processes:

(8) The red chip 103 and the infrared chip 104 are temporarily placed onthe submount 116 while vacuum-sucked by the collets 105, 106;

(9) Contact probes (not shown) are brought into contact withinterconnections which are formed on the submount 116 and havecontinuity with the red chip and the infrared chip and the contactprobes and the respective collets are energized to allow the two chipsto emit light;

(10) The light-emission points 117, 118 of these two chips arerecognized by one camera 119 for recognizing a distance between thelight-emission points, the distance between the light-emission points ofthe two chips and tilting angles of light emission axes of the twolight-emission points are detected and compared with prescribedpositions and shift amounts from the references are detected;

(11) If there is a shift, electricity is turned off, the collet israised and the collet is driven to correct the chip position to thereference light-emission point position by applying a voltage matchingthe shift amount to a piezo-electric element provided to each of colletheads for a red chip and an infrared chip;

(12) After the positions are corrected, the collets are lowered again,processes (9)-(11) are repeated a prescribed number of times and theshifts are corrected until the distance between the light-emissionpoints of the two chips is within the range according to aspecification;

(13) The position correction is repeated a prescribed number of timesand if specification accuracy cannot be obtained, the bonding procedureis deemed as an error and processed as such;

(14) When the specification accuracy is obtained, the contact probes areraised, the submount 116 is heated while both the collets 105, 106 arelowered and the red chip and the infrared chip 103, 104 are bonded tothe submount 116 by thermo-compression bonding;

(15) After bonding is completed, processes (9) and (10) are performedagain to confirm position accuracy; and

(16) The collets 105, 106 are raised and returned to the start positionof the fixed-point.

In the above process (11), when the position accuracy of the submount116 and the two chips is not so important, one laser chip position canbe used as a reference to correct only the position of the other laserchip. That is, highly accurate correction can be achieved by providing apiezo-electric element adjustment mechanism 123, 124 only to the bondinghead of the chip whose position is corrected.

In the process (12), the distance between the light-emission points ofthe two chips can be determined arbitrarily according to a specificationof the semiconductor laser device or the like. The number of times ofrepetition can also be arbitrarily determined.

Normally, vacuum-suction by the collet is continued during bonding.However, vacuum-suction by the collet can be stopped and the collet canbe raised in the middle of heating in the above process (14) so that theheat transmitted to the chip does not escape.

Furthermore, process (16) can be omitted.

Furthermore, position correction on the intermediate stage and positioncorrection on the bonding stage can be performed at the same time byproviding a pair of collets both for an intermediate stage and a bondingstage. Thus, the apparatus tact can be shortened.

EXAMPLES

FIG. 7 shows a block diagram of the two-chip bonding apparatus of thepresent invention. FIG. 8 shows one embodiment of the invention.Examples of the present invention are explained with reference to thesedrawings, but the present invention is not limited to the followingexamples.

Example 1

Two-chip bonding processes for fabricating a two-chip semiconductorlaser device having a specification distance between the light-emissionpoints of 100 μm by using tilted-type collets according to the presentinvention are described below.

A. Position Correction on Intermediate Stage

First, a red chip 103 and an infrared chip 104 were removed from a wafersheet 101 and 102, respectively, by usual pickup processing using aconventional technique as shown in FIG. 7 and placed on respectiveintermediate stages 109, 110.

Subsequently, chip shift amounts x and y from the chip referenceposition were detected by a profile recognition camera 111, 112. Also,an angular shift amount θ of each light-emission axis from the referencedirection was detected by a light-emission point recognition camera 113,114. The intermediate stage 109, 110 was moved by the shift amounts x,y, θ on the basis of the detection data to correct the chip position tothe reference position (FIG. 9).

Here, the direction of the light-emission axis of a laser emitted fromthe chip is assumed as a Y direction. The vertical direction of the chipis assumed as a Z direction. The direction perpendicular to the YZ planeis assumed as an X direction.

Processes of correcting shifts of the chip position and angle by profilerecognition and light-emission axis recognition on the intermediatestage are explained in detail below by using a red chip as an example(FIGS. 10-12).

I. Correction of Shift by Chip Profile Recognition

First, chip profile is recognized by using a CCD camera (profilerecognition camera 111) capable of recognizing a chip profile from above(FIG. 10A). To make the resolution of the profile recognition camera 111as high as possible, the magnification is adjusted so that only thevicinity of a laser outgoing end surface of the chip can be enlarged andobserved (FIG. 10B). The position of an outgoing surface 128 and bothside portions 129 of the chip are detected in the profile (FIG. 10C) andshift amounts x and y from the reference position and angular shiftamount θ from the reference direction are calculated. The calculatedshift amounts from the reference converted to motor movement amounts.The intermediate stage is moved to the reference position and thereference direction to correct the laser chip position in the X, Y and Θdirections.

II. Correction of Angle by Laser Light-emission Axis Recognition

The laser outgoing direction 130 may be tilted with respect to thereference direction only with shift correction by profile recognition ofthe chip shape as shown in FIG. 10. Therefore, angular correction bylight-emission axis recognition was further performed.

First, the chip light-emission point position was detected by using aCCD camera (light-emission point recognition camera 113) capable ofobserving the laser light-emission point 117 from the laser outgoingsurface side and a horizontal position (x₁, z₁) on the outgoing surfacewas determined while the outgoing surface was focused (FIG. 11A). Atthis time, the origin of the XZ plane is not limited, but was set at thecenter of the screen here.

This light-emission point recognition camera 113 can be driven in the Ydirection to detect a focused light-emitting position (FIG. 9).Therefore, while the camera was driven by steps in the Y direction, thelaser light-emission point was observed and the beam diameter wasmeasured by changing the y value (FIGS. 11B and 11C). Since the beam onthe laser outgoing surface is spread laterally along an active layer ofthe laser chip, the beam shape is long sideways. Therefore, in thepresent invention, the beam width in a direction perpendicular to theactive layer, that is, the Z direction was assumed as a “beam diameter”.

Subsequently, on the basis of the measured value obtained as describedabove, the relationship of the y value and the beam diameter wasapproximated by the quadratic function by using the least square method.A y value giving the smallest beam diameter in this approximate equationwas assumed as y₁ (FIG. 11C).

While the light-emission point camera from the detected y₁ was furtherdriven in the Y direction by Δy, the light emitting level was controlledup to the level where the light emitting level was not saturated. Thelaser light-emission point was observed and the horizontal position x₂on the outgoing surface was detected. A tilting angle θ of thelight-emission axis was calculated by using the following equation (1)(FIG. 11D). $\begin{matrix}{\Theta = {\tan^{- 1}\left( \frac{{X2} - {X1}}{\Delta \quad y} \right)}} & (1)\end{matrix}$

Correction amounts were calculated from the relationship of thereference position and detected positions and the intermediate stage 109was moved in the X, Y and Θ directions.

FIGS. 12A-12D show a state after recognition and correction of thelight-emission points when this procedure was repeated and a prescribedconvergent value was obtained. Shifts of the infrared chip were alsocorrected similarly.

The red chip and the infrared chip whose position and angle werecorrected were vacuum-sucked by the collets 105, 106 and transferredthrough fixed points onto the submount 116 placed on a bonding stagefrom left and right, respectively.

B. Final Position Correction on Bonding Stage

Position correction on the bonding stage is explained in detail below.Methods for performing this correction include absolute positioncorrection, where both the chips are moved to absolute positions withrespect to the submount, and relative position correction, where thelight-emission point of one chip is used as a reference and only theother chip is moved. In this example, the absolute position correctionwas performed.

While the red chip and the infrared chip transferred through fixedpoints to the bonding stage were vacuum-sucked, the collets 105, 106were lowered. The red chip and the infrared chip 103, 104 weretemporarily placed on the submount 116. Then, the respective collets105, 106 and the ground on the submount 116 were energized and the twosemiconductor laser chips 103, 104 were allowed to emit light.

The light-emission points 117, 118 of the two semiconductor laser chipswere recognized by a light-emission point CCD camera (camera 119recognizing a distance between the light-emission points) capable ofobserving the points from the side of one laser outgoing surface.

A difference in the Z-direction position recognition due to a differencein the wavelength of each chip was eliminated by using a lens 131without chromatic aberration as an optical system of this light-emissionpoint CCD camera. The camera 119 recognizing a distance between thelight-emission points is constituted so as to be driven in the Ydirection to detect a focused light-emitting position (FIG. 13).

The distance between the two light-emission points and the tiltingangles of the light-emission axes of the two semiconductor laser chipsdetected by the camera 119 recognizing a distance between thelight-emission points were compared with the reference values and theshift amounts from the reference values were measured. The positions ofthe two chips were corrected on the basis of the results. FIG. 14 showsa state before and after the position correction by recognition of thedistance between the light-emission points.

First, the laser light-emission points 117, 118 were observed by thecamera 119 recognizing a distance between the light-emission points. Thehorizontal positions (x₃, z₃) and (x₄, z₄) with respect to the outgoingsurface were detected and the distance L′ between the two points werecalculated by using the following equation (2). $\begin{matrix}{L^{\prime} = \sqrt{\left( {{X4} - {X3}} \right)^{2} + \left( {{Z3} - {Z4}} \right)^{2}}} & (2)\end{matrix}$

Subsequently, while the camera 119 recognizing a distance betweenlight-emission points was driven by steps in the Y direction, the laserlight-emission points 117, 118 were observed and the beam diameter wasmeasured by changing the y value (FIG. 14). Subsequently, on the basisthe measured value obtained as described above, the relationship betweenthe y value and the beam diameter was approximated by a quadraticfunction by using the least square method. The y values giving thesmallest beam diameter for the red chip and the infrared chip wereassumed as y₃ and y₄, respectively.

Each of the chips was moved in the X and Y directions by a bonding headwith a piezo-electric element which can be driven along two axes of theX and Y directions from the two detected light-emission points and thepositions were repeatedly corrected until the distance L′ between thetwo points became the reference value L (100±2 μm). Or, correction canbe performed so that X matches the reference value.

This procedure was repeated until the prescribed convergent value wasobtained and the positions of both the two chips were preciselycorrected by a high resolution.

In this example, the positions of both the red chip and the infraredchip were corrected, but, for example, relative position correction,where the red chip is used as a reference and only the infrared chip iscorrected, can be performed.

Then, the collets were raised, shifts were corrected by applying avoltage corresponding to the shift amount to the piezo-electric elementsprovided to the respective bonding heads for the red chip and theinfrared chip and the chips were moved to the respective referencelight-emission point positions.

When shifts were detected again, it was confirmed that the positionswere within prescribed accuracy. Then, bonding was performed.

A two-chip semiconductor laser device having the distance between thelight-emission points of 100±2 μm in accuracy was obtained.

Example 2

A procedure similar to Example 1 except for using eccentric-type collets17 of the present invention as the collets was taken to fabricate atwo-chip semiconductor laser device.

A two-chip semiconductor laser device having the distance between thelight-emission points of 100±2 μm in accuracy was obtained.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method of fabricating a semiconductor laserdevice wherein two semiconductor laser chips 12, 13 are die-bonded onone submount 116, comprising processes of placing the semiconductorlaser chips on intermediate stages 109, 110, allowing the semiconductorlaser chips on the submount 116 to emit light and measuringlight-emission point positions and transferring the semiconductor laserchips through fixed points to prescribed positions on the submount 116.2. The method of fabricating a semiconductor laser device according toclaim 1, including a process of measuring light-emission point positionsand light-emission axis directions of the semiconductor laser chipsplaced on the intermediate stages 109,
 110. 3. The method of fabricatinga semiconductor laser device according to claim 2, including a processof correcting positions and directions of the intermediate stages 109,110 on the basis of the results of measuring the light-emission pointpositions and light-emission axis directions of the semiconductor laserchips placed on the intermediate stages 109,
 110. 4. The method offabricating a semiconductor laser device according to claim 1, includingprocesses of sucking the two semiconductor laser chips 12, 13 fromrespective wafer sheets 101, 102 or a chip tray by using collets 105,106, transferring the collets 105, 106 through fixed points by afixed-point transfer movement mechanism 120 and placing the twosemiconductor laser chips on the respective intermediate stages 109,110, correcting positions of the two semiconductor laser chips on therespective intermediate stages, sucking the two semiconductor laserchips again, transferring the chips through fixed points and mountingthe chips on the submount 116, energizing the two semiconductor laserchips on the submount 116 to allow the chips to emit light and measuringa distance between the light-emission points of the two chips.
 5. Themethod of fabricating a semiconductor laser device according to claim 4,including a process of transferring the two semiconductor laser chipsonto the submount through fixed points and then correcting the chippositions on the basis of the measured distance between thelight-emission points by a movement mechanism 123 for fine XY movementprovided separately from the fixed-point transfer movement mechanism. 6.The method of fabricating a semiconductor laser device according toclaim 4, including processes of allowing the two semiconductor laserchips to emit light on the submount at the same time, measuring adistance between light-emission points and using one light-emissionpoint as a reference and moving the other chip to a prescribed positionon the basis of the measurement data.
 7. The method of fabricating asemiconductor laser device according to claim 4, including a process ofallowing the two semiconductor laser chips to emit light on thesubmount, measuring a distance between the light-emission points andmoving both the chips to prescribed positions by using light-emissionpoint positions predetermined for both the semiconductor laser chips asreferences on the basis of the measurement data.